The invention concerns an electromagnetically releasable friction safety brake with two brake components that are independent from one another.
For safety reasons official regulations often specify that two separate braking systems be provided in plant and machinery so that if one braking system fails the necessary safety is still provided. This is particularly the case with elevators and lifts in accordance with lift regulation TRA200 and EN81.
In document DE-U-295 10 828 in the name of the firm Chr. Mayr. GmbH & Co KG. two brakes are built together in one unit. This is a cost effective and space saving arrangement of providing two separate and independent brakes.
The known arrangement includes two armature discs, two brake discs, two spring arrangements to urge the armature discs against the brake friction plates and a single electromagnet with a magnetic solenoid in the middle between the armature discs and the brake friction plates.
This known brake is functionally effective but consists of very many components.
Document EP-A-0 078 944 shows an electromagnetically released friction safety brake with a single brake disc. In this arrangement the magnetic solenoid is axially movable in the magnet housing.
Document U.S. Pat. No. 3,446,322 concerns an electromagnetic clutch with an independently driven auxiliary clutch or brake with two concentrically arranged magnetic solenoids and a single brake disc.
Document U.S. Pat. No. 4,878,568 includes a description of an electromagnetic clutch-brake assembly with a single clutch plate and a single brake disc.
From document DE-C-300 941 it is known to provide a spring brake which is released by the force of an electromagnet with a single armature disc and a single brake disc which has arranged on both sides brake pads. In this arrangement the armature disc and the magnet housing are supported in such a way that they are movable axially and are subject to the force of springs of various strengths acting in opposite directions of which the stronger is the brake spring.
As the arrangement described in this document only has a single brake disc it does not comply with the safety requirements of regulations TRA200 and EN81. There are also no indications in this document as to how its subject matter could be modified to fulfill the safety requirements without a disproportionate amount of technical engineering resources.
Document EP-A-0 465 831 relates to a safety disc brake for a lift with two-part systems which work mechanically completely separately from one and other. The part systems are in the form of two identical brake levers each with a separate actuating spring that are supported on a common spring reaction center that is in turn fixedly attached to a part of the machine. The releasing function of the brake is achieved by means of a cup shaped electromagnet which is firmly attached to a brake lever. The fixing of the cup shaped electromagnet and the armature disc on the brake lever are adjustable so that the armature disc is always pulled exactly parallel by the cup shaped electromagnet.
The subject of EP-A-0 465 831 however requires considerable resources i.e. is built from a relatively large number of components and needs a relatively large space. It is also a disadvantage that the brake of EP-A-0 465 831 cannot be released manually.
Document DE-C-29 01 784 discloses adjusting apparatus for the air gap of an electomagnetically actuated disc brake in which the magnet housing is axially slidable with the help of the adjusting components on axially arranged pins that are fixedly attached to the machine housing.
In document DE-U-17 68 425 in connection with a brake with a brake releasing magnet the prior art is described as including a magnet housing that is axially slidable.
Document DE-U-19 14 395 concerns an arrangement for releasing in an emergency an electromagnetic disc spring brake by means of a releasing lever.
In the article by W Baumann "Bauarten und Eigenschaften Elektromagnetisch geluftete Bremssen und Stoppmotoren" (constructional types and characteristics of electromagnetically released brakes on stop motors) in "Konstruktion", 21,1969,H.4.pages 137-147 teaches that in such brakes a manual release can be provided which uses a stirrup which spans the brake by 180 degrees. Another manner of manual release is achieved by pressing together pins that are mounted on the brake linings to the right and left of the energizing winding.
In the four last mentioned documents there is no indication how the equipment described therein could be used in a safety brake with two brake discs.